Many of the helicopters being operated today embody a twin-engine power plant system which not only enhances the normal flight capabilities of a helicopter but also provides sufficient power to facilitate continued flight operations in safety under emergency conditions, such as in the event of a one-engine-inoperative (OEI) condition, e.g. a single engine failure.
The power plant in a modern helicopter is typically a gas turbine engine which usually operates within a normal rated power output range. Such engines are capable of producing power at a level significantly above the normal rated power range, however operation in this elevated power output greatly reduces the life expectancy of certain critical components such as the turbine blade, etc. Operation of a twin-engine helicopter in a OEI event necessitates relaxing of normal engine control criteria and allows the helicopter operator to demand and receive power from the remaining operating engine at levels in excess of the normal operating range. The shift in control logic is justified in such emergency situations for obvious safety reasons.
The training of helicopter pilots for engine failure operation has long caused problems for instructors and helicopter operators. The objective of initial pilot certification and pilot referential training is to ensure that pilots achieve and maintain a high degree of proficiency in all aspects of helicopter flight operations, including emergency procedures such as OEI flight operations. Such proficiency is typically achieved by repetitive training conducted under actual flight conditions, e.g. actual flight envelopes, actual gross weights (based on pressure altitude and ambient temperature), actual power settings, and actual cockpit instrument displays. Realistic training in OEI flight operations conventionally requires the pilot to temporarily disable the fuel control on one engine, reducing it to an idle condition effectively with a zero power output, and then operate the other engine within its elevated emergency rated power range. As noted above, such emergency power operation shortens the life expectancy of the engine, thereby increasing the frequency of extensive maintenance.
Helicopter gas turbine engines are rated by manufacturers and regulatory agencies for each permitted mode of operation. The rating of an engine establishes allowable time limits for operation at various power levels. Such levels may range from continuous at a normal or part-throttle levels, to the higher emergency power levels under certain time limits, such as 30 second/2 minute and/or 2.5 minute ratings. One factor in determining a one-time emergency limited rating for an engine, is the frequency with which the engine is expected to deliver such elevated levels of power. The realistic flight training method discussed above requires repeated use of emergency power during training exercises, resulting in a lower power level than would be allowable for a one-time actual emergency use.
An alternative commonly used within the industry is to reduce the weight of the helicopter to a minimum, and to operate the one engine at a flight idle power level with the other engine being controlled within its normal operating range. The cockpit displays are however, biased to indicate simulated maximum emergency power ratings, based on the weight biasing factor, in order to simulate the dynamics of an aircraft in a fully loaded condition. One example of this type of training method is disclosed in U.S. Pat. No. 5,873,546, issued to Evans et al. on Feb. 23, 1999.
One disadvantage of the prior art training methods results from operation of the helicopter with one engine in an idle condition. Should for any reason the power producing engine experience an unplanned failure, requiring the idling engine to be brought up to a full power state, the helicopter would experience a period of time in which the total available power is extremely low, thereby restricting maneuverability and possibly resulting in operating outside of safety margins.
Another conventional approach involves conducting OEI flight procedures training, utilizing both engines operating at an intermediate power output rating. In this approach, each engine is operated at a reduced power rating so that both engines in combination provide a power output at the intermediate power output rating that is equivalent to the power output provided by a single operative engine operating under a maximum emergency power rating. One example of this approach is disclosed in U.S. Pat. No. 4,831,567, issued to Lea on May 16, 1989 and assigned to the same assignee as this application.
Nevertheless, further an improved OEI training method is desirable to simulate an actual OEI situation.